Answer
$\dfrac{-8}{a^3}$
Work Step by Step
RECALL:
(i) $a^m \cdot a^n = a^{m+n}$
(ii) $a^{-m} = \dfrac{1}{a^m}, a \ne0$
Multiply the coefficients by each other and the variables by each other to obtain:
$=[4 \cdot (-2)] \cdot a^{2+(-5)}
\\=-8a^{-3}$
Use rule (ii) above to obtain:
$=-8 \cdot \dfrac{1}{a^3}
\\=\dfrac{-8}{a^3}$
